Question

Given, Sodium= 16.1%, Chlorine= 4.2%, Hydrogen= 7% and Oxygen= Rest. If all the hydrogen are used in formation of water of crystallization, find the molecular and the empirical formula of the crystallized salt.

Answer 1

percentage mass of sodium , Na = 16.1%

percentage mass of chlorine , Cl = 4.2%

percentage mass of hydrogen, H = 7%

percentage mass of oxygen , O = 100- (16.1 + 4.2 + 7) = 72.7%

finding percentage - atomic mass ratio

sodium ⇔ 16.1/23 = 0.7

chlorine ⇔ 4.2/35.5 = 0.1183

hydrogen ⇔ 7/1 = 7

oxygen ⇔ 72.7/16 = 4.54

now finding simple ratio of percentage-mass ratio

Na : Cl : H : O ⇔ 0.7 : 0.1183 : 7 : 4.51

= 0.7/0.1183 : 0.1183/0.1183 : 7/0.1183 : 4.51/0.1183

= 5.917 : 1 : 59.17 : 38.12

≈ 6 : 1 : 60 : 38

so, empirical formula of compound is $Na_6ClH_{60}O_{38}$

a/c to question, all the hydrogen are used in formation of water of crystallisation.

so, molecular formula of compound is $Na_6ClO_8.30H_2O$